The aim of this study was to examine pulmonary function after acute lymphoblastic leukaemia in childhood and identify risk factors for reduced pulmonary function. We studied a population-based cohort of 94 survivors of acute lymphoblastic leukaemia in childhood who were in first remission after treatment without spinal irradiation or bone marrow transplantation. Pulmonary function test results were compared with reference values for our laboratory, based on 348 healthy subjects who had never smoked from a local population study. A median of 8 years after cessation of therapy (range 1-18 years) the participants had a slight, subclinical, restrictive ventilatory insufficiency and reduced transfer factor and transfer coefficient. The changes in lung function were related to younger age at treatment and to more dose-intensive treatment protocols that specified more use of cranial irradiation and higher cumulative doses of anthracyclines, cytosine arabinoside and intravenous cyclophosphamide than previous protocols. We conclude that, 8 years after treatment without bone marrow transplantation or spinal irradiation, survivors of childhood acute lymphoblastic leukaemia in first remission were without pulmonary symptoms but had signs of slight restrictive pulmonary disease including reduced transfer factor. The increased dose intensity of many recent protocols for childhood acute lymphoblastic leukaemia may lead to increased late pulmonary toxicity.